U.S. Pat. Nos. 4,127,209 to Ruben, 4,416,739 to Turner and 4,787,962 to Temprano all describe methods for electroplating a layer of nickel onto titanium and titanium base alloys. Turner indicates that it is difficult to achieve good adhesion between the titanium substrate and the layer of electroplated nickel because an oxide film is typically present on the surface of the substrate. Turner's invention is to use an aqueous solution of hydrofluoric acid and formamide to remove to oxide. Ruben removes the oxide by connecting the substrate as the cathode in an acid solution such as sulfuric acid, and then forming a layer of titanium hydride on the substrate. Temprano pickles the substrate surface with a 95% sulfuric acid solution. Other prior art methods for removing the oxide scale include a solution containing hydrofluoric acid and nitric acid.
While the aforementioned methods may be successful with some titanium alloys, they are not useful on some specialty titanium alloys of the type used in the gas turbine industry. Accordingly, workers in this field seek improved techniques for applying electroplated layers of nickel onto state-of-the-art titanium alloys. This invention satisfies such a need.